Poster Presentations: Wednesday, November 3, 2010 |

Effects of Increased Chemostimulation on the Relationship Between Increasing Breathlessness Intensity and Increasing Neural Respiratory Motor Drive (Diaphragm EMG) During Exercise in Healthy Older Humans FREE TO VIEW

Dennis Jensen; Ruifa Li, MSc; Denis E. O'Donnell, MD; Yuanming Luo, MD
Author and Funding Information

Queen's University, Kingston, ON, Canada

Chest. 2010;138(4_MeetingAbstracts):567A. doi:10.1378/chest.10921
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PURPOSE: The neurophysiological underpinnings of exertional breathlessness are only partially understood, but the awareness of increased neural respiratory motor drive is likely contributory. Therefore, the purpose of this study was to examine the effects of increased chemostimulation on the relationship between increasing breathlessness intensity ratings and increasing diaphragm EMG (EMGdi) activity - an index of neural respiratory motor drive - during strenuous exercise in humans.

METHODS: Eleven healthy, older (56.5±1.6 yrs, mean±SEM; 8 women) volunteers with normal baseline pulmonary function (FEV1=102±5% predicted, FEV1/FVC=102±2% predicted) performed symptom-limited incremental cycle exercise tests under one of two conditions, randomized to order: unloaded control (CTRL) and 500 mL of dead space loading (DSL). Ventilatory (breathing pattern, end-tidal PCO2 {PETCO2}), respiratory mechanical/muscular (esophageal pressure {Pes} and EMGdi) and breathlessness intensity responses were measured at rest and during exercise.

RESULTS: Compared with CTRL, DSL reduced exercise performance: peak V'O2, peak work rate and the duration of loaded pedaling decreased by ~20%, 22% and 24%, respectively (all p<0.004). At the highest equivalent work rate (67±7 watts) under DSL vs. CTRL conditions: PETCO2, minute ventilation (V'E), tidal volume, breathing frequency, contractile respiratory muscle effort (tidal Pes swing expressed as a % of maximal inspiratory pressure {tidal Pes/PImax}), neural respiratory motor drive (EMGdi expressed as a % of maximal EMGdi {EMGdi/EMGdi,max}) and breathlessness intensity ratings increased by 7.3 mmHg, 17.2 L/min, 0.21 L, 6.5 breaths/min, 17.2 %PImax, 19.2 %EMGdi,max and 2.2 Borg units, respectively (all p<0.003). In contrast, DSL had no demonstrable effect on (i) the relationship between breathlessness intensity and each of EMGdi/EMGdi,max, tidal Pes/PImax and V'E and (ii) the inter-relationships between EMGdi/EMGdi,max, tidal Pes/PImax and V'E during exercise.

CONCLUSION: DSL-induced increases in exertional breathlessness reflected the awareness of increased neural respiratory motor drive (EMGdi/EMGdi,max), which in turn increased V'E and tidal Pes/PImax responses to exercise.

CLINICAL IMPLICATIONS: Increases in neural respiratory motor drive contribute importantly to the genesis of activity-related breathlessness in health and presumably also in cardiopulmonary disease.

DISCLOSURE: Dennis Jensen, No Financial Disclosure Information; No Product/Research Disclosure Information

12:45 PM - 2:00 PM




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